Matt Ward

ASP.NET 5 and DNX support in Xamarin Studio

Xamarin Studio and MonoDevelop now have support for ASP.NET 5 and DNX with an alpha release of the DNX addin.

DNX web project in Solution window

The core part of the addin that communicates with the DNX host is taken directly from OmniSharp and is used mostly unchanged.


  • Project templates for console, library and web applications
  • Code completion
  • Debugger support with Mono 4.3
  • NuGet integration
  • Solution window integration


  • MonoDevelop and Xamarin Studio 5.9 and later versions.
  • ASP.NET 5 RC 1 Update 1 and earlier versions.

Installing ASP.NET 5

ASP.NET 5 needs to be installed separately before using the DNX addin. There are instructions on on how to do this for Mac, Linux and Windows.

Installing the addin

The addin is currently available from MonoDevelop’s Add-in Repository in the alpha channel. In Xamarin Studio open the Add-in Manager and select the Gallery tab. Click the repository drop down and if Xamarin Studio Add-in Repository (Alpha Channel) is not displayed then click Manage Repositories. In the window that opens tick the check box next to Xamarin Studio Add-in Repository (Alpha Channel) and then click the Close button.

Enabling alpha channel addins

Back in the Add-in Manager dialog click the Refresh button to update the list of addins. Use the search text box in the top right hand corner of the dialog to search for the addin by typing in DNX.

DNX addin selected in Addin Manager dialog

Select the DNX addin and then click the Install button.

After installing the DNX addin you will need to restart Xamarin Studio before the project templates will be available in the New Project dialog.

Creating an ASP.NET 5 project

There are three project templates available for ASP.NET 5 in the New Project dialog.

New ASP.NET 5 project templates

Each of the project templates will create a solution and an .xproj file in the same way as Visual Studio 2015 does. The projects created should be compatible with Visual Studio 2015.

DNX console project in Solution window


When you create or open an ASP.NET 5 project the NuGet packages it uses will automatically be restored.

Restoring NuGet packages in Solution window

In the Solution window the dependencies show a warning icon if they are not resolved and the Dependencies folder shows a message that it is restoring the NuGet packages. Once restored you can expand the Dependencies folder and see the dependency hierarchy.

Dependency hierarchy in Solution window

If the DNX runtime being used by the solution is not installed then an error icon will be displayed next to the Dependencies folder.

Dependencies error icon in Solution window

Hovering the mouse over the error icon will show more information about the error.


When you build the solution or project any errors and warnings are displayed in the Errors window and in the text editor. No assemblies are generated when you build.

DNX build error in text editor

DNX build errors in Errors window


The main toolbar shows the currently selected command and the framework that will be used when the application is run. These are taken from the project.json file.

DNX commands in main toolbar

The screenshot above shows the main toolbar for a web project. There are three entries:

  • web
  • web DNX 4.5.1
  • web DNX Core 5.0

The first entry will run the web command and use the default runtime which will currently be DNX 4.5.1. The last two entries will run the web command but will explicitly run the application with the specified runtime.


Thanks to David KarlaĆĄ and Zoltan Varga there is support for debugging DNX applications with DNX 4.5.1 if you have Mono 4.3 installed.

Debugging a DNX application

Debugging ASP.NET 5 projects with the CoreCLR is not supported on Mac nor on Linux. Debugging ASP.NET 5 projects is not supported at all on Windows.

Adding NuGet Packages

To add a NuGet package to a project you can right click the Dependencies folder in the Solution window and select Add NuGet Packages, or alternatively you can double click the Dependencies folder.

Add NuGet Packages menu in Solution window

This will open up the Add NuGet Packages dialog. Installing a NuGet package using this dialog will add the NuGet package into the project.json file.

Note that using the Add Packages dialog from the Packages folder will not add the NuGet package into the project.json file and will instead download the package to the packages directory and update the packages.config file.

Adding Dependencies

Dependencies can also be added directly into the project.json file. Currently there is no code completion available in the project.json file but changes to the file are monitored and the Dependencies folder will be updated when items are added or removed. New NuGet package dependencies that are added will automatically be restored if they are missing.

Removing Dependencies

A dependency can be removed by selecting it in the Solution window, right clicking and selecting Remove, or by pressing the delete key.

Remove dependency menu in Solution window

Changing the active framework

In Visual Studio the active framework can be changed by selecting it from the drop down list at the top of the text editor. Currently using the drop down list at the top of the text editor to change the active framework is not supported in Xamarin Studio. Instead you can right click in the text editor, select Active Framework and then select the framework.

Active DNX framework context menu in text editor

The active framework affects the code completion provided in the text editor. In the screenshot below the active framework has been set to DNX Core and you can see that the DateTime type does not show ToShortDateString in its completion list.

Code completion for active DNX framework

You can also see that the code in the #if DNX451 block is grayed out since it is not used with the currently active framework.

DNX Output

Output from the DNX host and from OmniSharp can be seen in the DNX Output window. This window can be opened by selecting DNX Output from the View menu.

DNX Output window

By default only warnings and errors will be displayed in the DNX Output window. To see more or less information you can change the DNX output verbosity in preferences in the DNX – General section.

Known Issues

kqueue() FileSystemWatcher has reached the maximum number of files to watch

When opening a project with many source files, such as AutoFac, you may see the above FileSystemWatcher error message. To resolve this problem you can set the MONO_MANAGED_WATCHER to false:


Xamarin Studio will need to be run from the command line for this environment variable to be used.

project.json file formatting

When adding or removing dependencies from the Solution window will cause the project.json file to be reformatted differently compared to how Visual Studio 2015 formats the file.

Source Code

The source code for the addin is available on GitHub.

There is also a separate branch that supports MonoDevelop and Xamarin Studio 6.0.